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Avalanche Forecast

Archived

Feb 28th, 2013–Mar 1st, 2013

Alpine
Widespread avalanches certain.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural and human triggered avalanches likely.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Sea To Sky.

Confidence

Fair - Track of incoming weather is uncertain for the entire period

Weather Forecast

Thursday night/ Friday: Moderate to heavy precipitation. Strong to extreme SW winds. Freezing level around 1500-1800 m.Saturday: Light to moderate precipitation. Winds easing to moderate southerly. Freezing level around 1800 m, falling to 1000 m.Sunday: Lingering snow showers could bring up to 15 cm snow, then clearing up. Light winds. Freezing level around 1000 m.

Avalanche Summary

Recent reports include several human-triggered slab avalanches to size 2, involving wind slabs, recent storm snow weaknesses and the persistent weakness buried last week. Some events involving the persistent weakness were remotely triggered from as far as 50 m away. A size 3 slab failed naturally on the persistent weakness, wrapping around an entire north-facing bowl and running across a flat bench. A size 2.5 avalanche was triggered by a party of sledders on Sunday in the Brohm Ridge area, and left a man buried 1.8 metres below the surface. Check out the Forecaster blog for the full story. Activity seems to have slowed on Wednesday, but intense storm loading is expected to drive another avalanche cycle over the next few days.

Snowpack Summary

A potentially volatile weakness of surface hoar and/or a crust exists within the upper metre or so of the snowpack. Add an intense storm, with heavy precipitation rates, warming and very strong winds, and we have a good recipe for widespread avalanche activity. The lower snowpack is well settled.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.